The present invention is a process for the rearrangement of polyorganosiloxanes using solid, sulfonated polyethylene as a rearrangement catalyst. In a preferred process the solid, sulfonated polyethylene is in the form of hollow fibers through which the polyorganosiloxanes are passed to effect rearrangement.
It is known that polyorganosiloxanes can be prepared by rearrangement reactions, the silicon-oxygen-silicon bonds being rearranged virtually arbitrarily. Rearrangement reactions of polyorganosiloxanes are catalyzed by strong bases and strong acids. Polyorganosiloxane rearrangements catalyzed by strong acids and bases are frequently used in the industrial preparation of polyorganosiloxanes with a relatively high molecular weight from polyorganosiloxanes with a relatively low molecular weight, and vice versa.
The catalysts typically used for the rearrangement of polyorganosiloxanes are strong bases, such as alkali metal bases, for example lithium oxide, sodium hydroxide, potassium alkoxides, potassium silanolates, and cesium hydroxide; quaternary bases, such as tetraalkylammonium hydroxides and alkoxides and tetraalkylphosphonium hydroxides and alkoxides; and strong acids such as complex Lewis acids, hydrogen halide acids, sulfuric acid, boric acid, and trifluoromethylsulphonic acid. In addition, acid treated support materials such as carbon, silicates, and clays have been described as useful rearrangement catalysts for polyorganosiloxanes.
The "mobile" catalysts such as the alkali metal bases potassium hydroxide and cesium hydroxide; quaternary bases such as tetraalkylammonium hydroxide; and strong acids such as sulfuric acid and trifluoromethyl sulfonic acid typically require a process to neutralize the catalyst at the completion of the rearrangement process. This neutralization is necessary to provide for storage stability of the rearranged polyorganosiloxanes. Since many applications for polyorganosiloxanes, for example those used as electrical insulating oils, require pure, salt-free polyorganosiloxane it is necessary to remove these salts.
The present process provides an advantage of being simpler in comparison to those processes using mobile catalyst for rearrangement of polyorganosiloxanes. When the solid sulfonated polyethylene catalyst of the present process is used, the process of neutralization and the removal of the resulting salts are eliminated. The catalyst according to the present invention is either fixed in the reactor or it is retained by built-in fitments such as sieves. Therefore, the present process can be advantageously run as a continuous process with extended use of the solid sulfonated polyethylene rearrangement catalyst and with no need to neutralize the rearranged polyorganosiloxane product.
Litteral, U.S. Pat. No. 3,694,405 describes the use of a packed-bed of a macroreticular sulfonic acid cation exchange resin having a specific pore volume of at least about 0.01 cc per gram as a rearrangement catalyst for polyorganosiloxanes. Litteral teaches such resin can be prepared by sulfonating a reticulate copolymer of styrene and a polyvinylidene monomer, such as divinylbenzene, trivinylbenzene, as well as polyvinyl ethers of polyhydric alcohols, such as divinyloxyethane and trivinyloxypropane. The sulfonating agent can be concentrated sulfuric acid, oleum, sulfur trioxide or chlorosulfonic acid.
Finke et al., U.S. Pat. No. 4,310,679 teach the rearrangement of polyorganosiloxanes in the presence of a cation exchange resin, where the resin employs a polymer having side chains carrying sulfonyl groups and the carbon atoms carrying the sulfonyl groups also carrying at least one fluorine atom (e.g. Nafion.RTM., DuPont Corporation, Wilmington, Del.).
The present invention uses solid sulfonated polyethylene as a rearrangement catalyst for polyorganosiloxanes. The solid sulfonated polyethylene is a relatively low-cost material that can be easily separated from the polyorganosiloxanes. The solid sulfonated polyethylene rearrangement catalyst can be in the form of hollow fibers through which the polyorganosiloxanes are passed to effect rearrangement.